Absorbent nonwoven fabrics

ABSTRACT

A permanently absorbent nonwoven fabric comprises a web of fibers, a crosslinkable latex binder, and a surfactant consisting of at least one bis-alkyl sulfosuccinate having alkyl substituents containing 13-14 carbon atoms. The preferred surfactant is bis-tridecyl sodium sulfosuccinate, and the amount used is generally 0.2-10.0 weight percent of the total fibers and binder. The surfactant may be incorporated into the binder latex prior to, during, or after polymerization.

Unite States atet 1 Katz et al.

[ 1 Nov. 25, 1975 1 ABSORBENT NONWOVEN FABRICS [73] Assignee: NationalStarch and Chemical Corporation, Bridgewater, NJ.

22 Filed: Apr. 10, 1974 21 Appl. No.: 459,465

[52] US. Cl 428/290; 428/411 [51] Int. Cl. D06N 7/06 [58] Field ofSearch 117/140 A, 140 R, 161 UZ,

[56] References Cited UNITED STATES PATENTS 3,720,562 3/1973 Drelich117/140 Primary ExaminerRalph S. Kendall Assistant ExaminerChar1es R,Wolfe, Jr.

[57] ABSTRACT A permanently absorbent nonwoven fabric comprises a web offibers, a crosslinkable latex binder, and a surfactant consisting of atleast one bis-alkyl sulfosuccinate having alkyl substituents containing1314 carbon atoms. The preferred surfactant is bis-tridecyl sodiumsulfosuccinate, and the amount used is generally 0.2-l0.0 weight percentof the total fibers and binder. The surfactant may be incorporated intothe binder latex prior to, during, or after polymerization.

12 Claims, No Drawings ABSORBENT NONWOVEN FABRICS BACKGROUND OF THEINVENTION This invention relates to so-called nonwoven fabrics of thetype composed of a loosely assembled web of fibers bound together by ,alatex binder. Such bonded nonwoven fabrics have been formed byimpregnating, printing or otherwise depositing an adhesivebondingmaterial on a base web predominately comprising relatively long fibers,including those of textile length from about 0.5 inch to about 2.5inches or more. The base web of the nonwoven fibers to which the latexbinder is applied can be produced inexpensively and with low capitalinvestment by carding, garnetting, interlaying, paper-making procedures,or other known operations for which automation is possiblepThe operationof bonding the fibers in place is much less expensive than conventionalspinning and weaving. In comparison with woven fabric, the bondednonwoven fabrics can be made in a much greater range of thicknesses,with a more homogeneous structure and no unravelling tendency, and withgreater water absorbency, porosity and resiliency, when required.

To improve the absorbency ofthe bonded nonwoven fabrics, variousemulsifiers have been used during the emulsion polymerization to producethe binder, and various wetting agents have been added to theimpregnated medium by which the binder is applied to the fiber web. Forexample, bonded nonwoven fabrics for use as household wipes wipingclothes to remove and pick up liquids, wash furniture and cars, cleankitchens, etc. are typically absorbent because of the presence ofanionic surfactants such as dioctyl sodium sulfosuccinate or sodiumdodecyl benzene sulfonate. Such bonded nonwoven fabrics have not provento be entirely satisfactory in use because the emulsifiers and wettingagents are generally easily extractable by water rinsing, machinewashing and/or steam sterilization, thus rendering the fabricnonabsorbent. Such fabrics are especially not satisfactory for thecommon industrial, hospital and consumer wages where high absorbencyafter repeated usage is required.

Accordingly, it is an object of the present invention to provide abonded nonwoven fabric incorporating a surfactant which resistsextraction by water rinsing and even steam sterilization.

It is another object to provide such a fabric which is formed by bondingfibers with a crosslinkable binder' latex incorporating a'specificsurfactant which resists extraction.

It is a further object to provide such a fabric which comprises fibersset with a commercially available binder to which a specific surfactanthas added to impart permanent absorbency characteristics to the fabric.

SUMMARY OF THE INVENTION It has now been found that the above andrelated objccts of the present invention are obtained in an absorbentnonwoven fabric comprising a web of fibers, a crosslinkable binder, andat least one surfactant consisting of at least one bis-alkylsulfosuccinate having alkyl substituents containing 13-14 carbon atoms.The surfactant is preferably bis-tridecyl sodium sulfosuccinate havingbranched alkyl substituents, and the crosslinkable binderis preferablyan emulsion copolymer of at least two a,B-monoethylenically unsaturatedmonomers, one an effectively monofunctional monomer and the other aneffectively polyfunctional and hence crosslinkable comonomer. Generallythe fabric includes about 5 to about lOO weight percent of the binder(based on the fiber weight), and about 0.2 to about 10.0 weight percentof the surfactant (based on the weight of the fibers and binder).

A preferred fabric comprises a loosely assembled web of fibers, about 10to about weight percent (based on the fibers) of crosslinkable binder,and about 0.3 to about 2.0 weight percent (based on the weight of thefibers and binder) of bis-tridecyl sodium sulfosuccinate having at leastone branched alkyl substituent. The binder is preferably comprised of atleast one a,B monoethylenically unsaturated monomer selected from thegroup consisting of alkyl acrylate, vinyl acetate, ethylene, vinylchloride, and mixtures thereof, and at least one a,B-monoethylenicallyunsaturated polyfunctional crosslinkable comonomer selected from thegroup consisting ofa crylamide, N-methylol acrylamide and isobutoxymethyl acrylamide.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The absorbent nonwovenfabric of the present invention is comprised of a loosely assembled webof fibers, a crosslinkable polymeric latex binder formed of at least onea,B-monoethylenically unsaturated monofunctional monomer and at leastone a,B-monoethylenically unsaturated polyfunctional crosslinkingcomonomer, and at least one surfactant of the present invention. Variouscatalysts, emulsifying and wetting agents, protective colloids,buffering agents, plasticizers, thermosetting resins and the like knownto those skilled in the art may optionally be used during formation ofthe binder or fabric.

THE FIBERS The starting layer or mass can be formed by any one of theconventional techniques for depositing or arranging fibers in a web orlayer. These techniques include carding, garnetting, air-laying, and thelike. Individual webs or thin layers formed by one or more of thetechniques can also be laminated to provide a thicker layer forconversion into a fabric. In general, the fibers extend in a pluralityof diverse directions in general alignment with the major plane of thefabric, overlapping, intersecting and supporting one another to form anopen, porous structure. When reference is made to cellulose fibers,those fibers containing predominantly G l-L 0 groupings are meant. Thus,examples of the fibers to be used in the starting layer are the naturalcellulose fibers, such as cotton, silk and hemp, and the syntheticcellulose fibers, such as rayon, and regenerated cellulose. Often thefibrous starting layer contains at least 50% cellulose fibers, whetherthey be natural or synthetic, or a combination thereof. Other fibers inthe starting layer may comprise natural fibers such as wool or jute;artificial fibers such as cellulose acetate; synthetic fibers such aspolyamides (i.e., nylon), polyesters (i.e., Dacron) .acrylics (i.e.,Dynel, Acrilan," Orlon) vpolyolefins (i.e., polyethylene, polyvinylchloride, polyurethane, etc. vinyl resin fibers (i.e., the copolymers ofvinyl chloride and vinyl acetate), siliceous fibers (i.e., glass andmineral wools), alone or in combination with one another.

3 The fibrous starting layer or web suitably weighs from about 100grains to about 2,000 grains per square yard and preferably weighs about200 grains to about 800 grains per square yard. This fibrous startinglayer, regardless of its method of preparation, is then subjected to atleast one of the several types of bonding op erations to anchor theindividual fibers together to form a self-sustaining web. Some of thebetter-known methods of bonding are overall impregnation or printing theweb with intermittent or continuous straight or wavy lines or areas ofbinder extending generally transversely or diagonally across the web andadditionally, if desired, along the web.

THE MONOMERS At least one a,,8-monoethylenically unsaturatedmonofunctional monomer forms the major part of the binder, generallyfrom about 85 to about 99, preferably from about 95 to about 98, weightpercent of such monomers based on the total binder monomers in thepolymerization.

The monomers useful as this component include vinyl esters of theformula:

wherein R is a C -C alkyl group, and preferably a C -C alkyl group.Representative of such vinyl esters are the preferred vinyl acetatecompound, as well as vinyl propionate, vinyl laurate, etc.

Other monomers useful as this component include the alkyl esters ofacrylic and methacrylic acid having the formula:

wherein R is a C,C alkyl group, and R is hydrogen or a methyl group.Representative of such alkyl esters are methyl acrylate, ethyl acrylate,butyl acrylate, methyl methacrylate, etc.

Still other monomers useful as this component include the C C dialkylesters of maleic, fumaric and itaconic acids (e.g., dibutyl maleate.dioctyl fumarate, etc.), styrene, vinyl chloride, vinylidenechloride,|etllylene and acrylonitrile.

The monomers useful as this component are effectively monofunctional atthe processing parameters utilized (i.e., the polymerizationtemperature, time, etc.) i.e., they enter into chain growth but notcrosslinking reactions.

The preferred monomers for this component are alkyl acrylates, vinylacetate, ethylene, vinyl chloride and mixtures thereof, If desired,mixtures of the above monomers may be utilized as this component. Thepreferred mixtures of monomers on a weight basis include a 50-100/0-50mixture of an alkyl acrylate (such as butyl acrylate) and vinyl acetate,a 60-100/0-40 mixture of vinyl acetate and ethylene, a 60-90/1040mixture of vinyl chloride and ethylene, and a 0-100/0-100 mixture ofvarious alkyl acrylates such as ethyl acrylate and butyl acrylate.

THE CROSSLINKING COMONOMERS At least one crosslinkinga,B-monoethylenically unsaturated polyfunctional comonomer forms a minorpart of the binder to effect crosslinking of the binder, generally fromabout 1 to about 15, preferably from about 2 to about 5, weight percentof such comonomers based on the total binder monomers (includingcomonomers) used in the polymerization.

The comonomers useful as this component include 1. acrylamide andmethacrylamide of the formula wherein R is hydrogen or a methyl group;ll. N-alkylol and alkyl ether derivatives of (I) having the formulawherein R is hydrogen or a methyl group,

R is hydrogen or a C -C alkyl group, and

R is (Cl-1 preferably a CH group; III. N-alkyl substituted derivativesof (I) having the formula wherein R is a hydrogen or a methyl group, and

R is a C C alkyl group; IV. hydroxy alkyl esters of acrylic ormethacrylic acid having the formula R is hydrogen or a methyl group, and

R is (Cl-I preferably a (Clh group; V. glycidyl alkyl esters of acrylicand methacrylic acid (e.g., glycidyl acrylate) having t e formula THESURFACTANT The surfactant useful in the practice of the presentinvention is a bis-alkylsulfosuccinate wherein the alkyl substituentseach contain 13-14 carbon atoms, preferably 13 carbon atoms. Thesurfactant is preferably an alkali metal salt of the bis-alkylsulfosuccinic acid, and at least one of the alkyl group substituents ispreferably branched. The preferred surfactant is bis-tridecyl sodiumsulfosuccinate, especially where at least one of the tridecyl groups isbranched. Similar compounds having lower alkyl groups substituents(e.g., 12 carbon atoms and less), especially straight chain lower alkylgroups, are rapidly extracted during rinsing, washing or steamsterilization; similar compounds with higher alkyl group substituents(e.g., 15 carbon atoms and up) are so insoluble as to interfere withtheir incorporation into the binder latex, or, when incorporated, do notimpart permanent absorbent properties to the fabric.

The amount of surfactant used is from about 0.2 to about 10.0,preferably about 0.3 to about 2.0 weight percent based on the combinedweight of the fibers and binder. The surfactant may be used alone or incombination with various emulsifying and/or wetting agents. It may beadded to the binder latex prior to polymerization, added intermittentlyor continuously during polymerization, or even added subsequent topolymerization.

THE CATALYST Various free-radical forming catalysts can be used incarrying out the polymerization of the monomers, such as peroxidecompounds. Combination type catalysts employing both reducing agents andoxidizing agents can also be used. The use of this type of combinedcatalyst is generally referred to in the art as redox polymerization" orredox system. The reducing agent is also often referred to as anactivator and the oxidizing agent as an initiator. Suitable reducingagents or activators include bisulfites, sulfoxylates, or othercompounds having reducing properties such as ferrous salts and tertiaryaromatic amines (e.g., N, N-dimethyl aniline). The oxidizing agents orinitiators include hydrogen peroxide, organic peroxides such as benzoylperoxide, t-butyl hydroperoxide and the like, persulfates such asammonium or potassium persulfate, perborates, and the like. Specificcombination type catalysts or redox systems which can be used includehydrogen peroxide and zinc formaldehyde sulfoxylate; hydrogen peroxide,ammonium persulfate, or potassium persulfate, with sodium metabisulfite,sodium bisulfite, ferrous sulfate, dimethyl aniline, zinc formaldehydesulfoxylate or sodium formaldehyde sulfoxylate.

In general, it is advantageous to utilize more watersoluble peroxides,such as hydrogen peroxide, rather than the more oil-soluble peroxides,such as t-butyl hydroperoxide, in the redox system catalyzing themonomer polymerization. Redox catalyst systems are described, forexample, in Fundamental Principles of Polymerization" by G. F. DAlelio(John Wiley and Sons, The, New York, 1952) pp. 333 et seq. Other typesof catalysts that are wellknown in the art can also be used topolymerize the monomers according to this invention, with or without theaddition of reducing agents or other activating materials.

The activator is ordinarily added in aqueous solution and the amount ofactivator is generally 0.25 to 1 times the amount of catalyst.

EMULSIFYING AGENTS The emulsifying agent can be any of the non-ionic oranionic oil-in-water surface active agents. In the following discussionof emulsifying agents, frequent reference will be made to a cloud pointof a particular agent. The cloud points which are recited are based on 1weight percent aqueous solutions of the agent. A relatively hy'drophobic agent is one having a cloud point below 190F. and a relativelyhydrophilic agent is one having a cloud point of 190F. or above.

A single emulsifying agent can be used or the emulsifying agents can beused in combination. When combinations of emulsifying agents are used.it is advantageous to use a relatively hydrophobic agent or a relativelyhydrophobic agent in combination with a relatively hydrophilic agent.The amount of emulsifying agent used is generally from about 0.1 toabout 10, preferably O.5-7.0, weight percent of the monomers used in thepolymerization.

Suitable nonionic emulsifying agents include polyoxyethylene condensatesrepresented by the following general formula:

R(-CHZCHZO),, H

where R is the residue ofa fatty alcohol, acid, amide, or amine havingfrom 10 to 18 carbon atoms or an alkyl phenol having from 10 to 18carbon atoms; and where n is an integer of 1 or above and preferablybetween 5 and 30. Some specific examples of polyoxyethylene condensateswhich can be used include polyoxyethylene aliphatic ethers such aspolyoxyethylene lauryl ether, polyoxyethylene oleyl ether,polyoxyethylene hydroabietyl ether and the like; polyoxyethylene alkarylethers such as polyoxyethylene nonylphenyl ether, polyoxyethyleneoctylphenyl ether and the like; polyoxyethylene esters of higher fattyacids such as polyoxyethylene laurate, polyoxyethylene oleate and thelike as well as condensates of ethylene oxide with resin acids and talloil acids; polyoxyethylene amide and amine condensates such asN-polyoxyethylene lauramide and N-lauryl-N-polyoxyethylene ethyl amineand the like; and polyoxyethylene thioethers such as polyoxyethylenen-dodecyl thioether.

Some examples of nonionic emulsifying agents which can be used include apolyoxyethylene nonylphenyl ether having a cloud point of between 126and 130F and marketed by GAF Corporation under the trademark lgepalCO-630," and a polyoxyethylene nonylphenol ether having a cloud point ofabout 212F. and marketed under the trademark Igepal C0-887. A similarpolyoxyethylene nonylphenyl ether having a cloud point of about 86F. ismarketed under the trademark Igepal CO-6l0 and is also a goodemulsifying agent. Another agent is a polyoxyethylene octylphenyl etherhaving a cloud point of between 80F and F. and marketed by Rohm & HaasCompany under the trademark Triton X-lOO." Yet another agent isnonylphenoxy polyethoxyethanol marketed under the trademark TritonX-305. Other emulsifying agents include a polyoxyethylene oleyl etherhaving a cloud point of between 80F. and 160F. and marketed under thetrademark Atlas (Ii-3915, and a polyoxyethylene lauryl ether having acloud point above F. and marketed under the trademark Brij 35".

The nonionic emulsifying agents which can be used according to thisinvention also include a series of surface active agents known asPluronics." The Pluronics have the general formula:

where a, b and c are integers between 1 and 100. As the ratio of b to aand c increases, the compounds become less water soluble or more oilsoluble and thus more hydrophobic. while as the ratio decreases thecompounds become more water soluble and less oil soluble. An example ofthis class is Pluronic L-64" which has a cloud point of about 140F. anda polyoxypropylene chain having a molecular weight of 1,500 to 1,800 anda polyoxyethylene content that is 40 to 50 percent of the total weightof the molecule. Another useful example is Pluronic F-68", apolyoxyethylene-polyoxypropylene glycol having a cloud point of about212F. and a polyoxyethylene content of about 80 to 90 percent of thetotal weight of the molecule.

A class of suitable emulsifying agents are a series of ethylene oxideadducts of acctylenic glycols sold commercially under the nameSurfynols. This class of compounds can be represented by the formula:

i-uocrncn y o )cmcruonn in which R and R are alkyl radicals containingfrom three to carbon atoms, R and R are selected from the groupconsisting of methyl and ethyl, and x and y are integers having the sumin the range of 3 to 60, inelusive.

Representative of the Surfynols are Surfynol 465 which is an ethyleneoxide adduct of 2,4,7,9-tetramethyl decynediol containing an average of10 moles of ethylene oxide per mole of the surface active agent.Surfynol 485 corresponds to Surfynol 465 but contains an average of 30moles of ethylene oxide per mole of surface active agent. Surfynol 485has a cloud point about 212F.

Anionic emulsifying agents which can be employed herein include anioniccompounds obtained by sulfonation of fatty derivatives such assulfonated tallow, sulfonated vegetable oils and sulfonated marineanimal oils. Commercially available emulsifiers of this group areTallosan RC, a sulfonated tallow marketed by General DyestuffCorporation; Acidolate, a sulfonated oil marketed by White Laboratories,lnc.; and Chemoil 412, a sulfonated castor oil marketed by StandardChemical Company.

Various sulfonated and sulfated fatty acid esters of monoand polyvalentalcohols are also suitable such as Nopco 2272R, a sulfated butyl esterof a fatty ester marketed by Nopco Chemical Company; Nopco 1471, asulfated vegetable oil marketed by Nopco Chemical Company; Sandozol N, asulfated fatty ester marketed by Sandoz, lnc.; and Stantex 322, an estersulfate marketed by Standard Chemical Products, Inc.

Sulfated and sulfonated fatty alcohols are also useful as an emulsifierand include anionic agents such as Duponal ME, a sodium lauryl sulfate;Duponal L142, a sodium cetyl sulfate; Duponal LS, a sodium oleyl sulfatewhich is marketed by E. l. DuPont de Nemours and Company; and Tergitol4, a sodium sulfate derivative of 7-ethyl-2-methyl, 4-undecanol,Tergitol 7, a sodium sulfate derivative of 3,9-diethyl tridecanol-6, andTergitol 08 a sodium sulfate derivative of 2 ethyl-l-hexanol, which aremarketed by Union Carbide Corporation, Chemical Division.

A particular useful class of anionic agents which can be employedcomprises the C to C alkyl and C to C cycloalkyl esters of alkali metalsulfoalkanedioic acids having from three to about six carbons. Examplesof these include diethyl sodium sulfosuccinate, di-n-octyl potassiumsulfosuccinate, dicyclohexyl lithium sulfoglutarate,di(methylcyclopentyl) sodium sulfoadipate, dicycloheptyl cesiumsulfomalonate, diamyl sodium sulfoadipate, etc. A useful member of thisclass is dioctyl sodium sulfosuccinate marketed by American Cyanamid Co.under the trademark "Aerosol-OT.

The half esterified, half ethoxylated derivatives of the aforementionedalkali metal sulfoalkanedioic acids are preferred emulsifiers. Theseagents have one of the carboxylic acid sites esterified with a C to Calkanol or C to C cycloalkanol, and the remaining carboxylic acid sitecondensed with from two to about 20 (preferably from eight to 16, andmost preferably from 10 to 12) ethylene oxide units per mole to add apolyethoxylol group. Examples of these are: hexyl polyethoxylol sodiumsulfosuccinate, isopropyl polyethoxylol potassium sulfoglutarate, decylpolyethoxylol lithium sulfoadipate, cyclohexyl polyethoxylol cesiumsulfomalonate, cycloheptyl polyethoxylol sodium sulfosuccinate,cyclooctyl polyethoxylol potassium sulfosuccinate, etc.

Another preferred anionic emulsifying agent is sodium dodecyl benzenesulfonate, commonly called SDBS and used in a 20 weight percentsolution.

OTHER POLYMERIZATION REAGENTS A protective colloid may optimally be usedto increase the adhesiveness of film prepared from the latex. When theprotective colloid is used, it is desirable to decrease the amount ofemulsifying agent used by an amount equivalent to the weight of theprotective colloid, since the latter also aids the stability of thelatex. This agent can be any of a wide range of compounds that isavailable for use as protective colloids, including many naturalsubstances such as casein, natural gums, gelatins, agar, dextrin andglobulin; suitably chemically modified polysaccharides such ashydrolyzed starch, hydroxyethyl cellulose, methyl and carboxymethylcellulose; and synthetic colloids such as polyvinyl alcohol, alkalimetal or ammonium salts of sulfonated polystyrene, water solubleinterpolymers of acrylic acid and 2-ethylhexyl acrylate, copolymers ofacrylamide and acrylic acid, partially hydrolyzed polyacrylamide havingfrom 10 to percent of its amide groups as carboxylic acid or alkalimetal carboxylate groups, etc. The polyvinyl alcohols, which areprepared by hydrolysis of polyvinyl esters, typically polyvinylacetate,are preferred protective colloids and can be used with from to 100percent, preferably from about to percent of the ester groups hydrolyzedto hydroxyl groups.

A buffering agent can be used, to maintain the pH at a value from about2.0 to 7.0, preferably from about 2.5 to 5.0, by periodic addition ofthe buffering agent. Suitable agents comprise the alkali metal orammonium salts of weak acids; e.g., sodium carbonate, sodiumbicarbonate, sodium acetate, potassium bicarbonate, lithium carbonate,potassium acid phthalate, potassium citrate, sodium acetate, potassiumacid phosphate, and others well-known in the polymerization art.

Various polymerization modifiers may optimally be used in smallquantities to modify the molecular weight of the copolymers'formedduring polymerization. For example, various polyfunctional agents, suchas divinyl benzene and allyl methacrylate, may be used to increasemolecular weight; various chain transfer agents, such as the mercaptansand alcohols, may be used to decrease molecular weight. I

THE POLYMERIZATION PROCESS The polymerization of the aforementionedmonomers is performed by emulsion polymerization, generally under batchconditions; however, continuous processing can be employed if desired.The reactor used for the polymerization can be a jacketed kettle havingstirring means with provisions to circulate a cooling medium through thejacket of the kettle to maintain the desired temperature. The aqueousmedium is stirred to maintain dispersion of the monomers and thecopolymer in the aqueous medium. I

A suitable emulsifying agent of the anionic or nonionic types, orcombinations thereof, is used in the polymerization. The amount ofemulsifying agent is generally from about 0.1 to about 10, preferablyfrom about 1 to about 5, weight percent of the monomers used in thepolymerization.

A water soluble, free radical catalyst such as a water soluble peracidor salt thereof is used as the initiating catalyst and this can be usedalone or in combination with an active reducing agent in a redox couple.The catalyst is used in concentration from about 0.01 to about 2,preferably from about 0.1 to about 0.5, weight percent of the monomersused in the polymerization.

The surfactant of the present invention is generally added to thepolymerization latex in an amount offrom about 0.2 to about 10.0,preferably 0.3-2.0, weight percent based on the combined weight ofbinder monomers and fibers.

If desired, the polymerization medium can also contain a minor quantityof aprotective colloid to improve the adhesiveness of the product,generally from about 0.1 to about 3.0, preferably 0.5-1.5, weightpercent based on the monomers used in the polymerization.

If desired, the polymerization medium can also contain a minor quantityof a buffering agent, generally from about 0.1 to about 0.5, preferably0.2-0.4, weight percent of the monomers used in the polymerization.

Polymerization is performed conventionallytypically at a temperature ofabout 30-90C, preferably 4070C, for sufficient time to achieve a lowfree monomer content; e.g:, from 1 to about 10 hours, preferably from 5to about 8 hours, to produce a latex having less than 3, preferably lessthan 1.5, weight percent free monomer.

The preferred procedure is a modified batch processing wherein the majoramounts of some or all the comonomers and emulsifier are charged to thereaction vessel after polymerization has been initiated. In this manner,control over the copolymerization of monomers having widely varieddegrees of reactivity can be ahieved.

It is preferred to add the a,B-monoethylenically unsaturated monomers(e.g., vinyl acetate) intermittently or continuously over thepolymerization period. The

a,B-monoethylenically unsaturated polyfunctional crossli'nkingcomonomers (e.g., N-alkyl methacrylamide or acrylamide) are preferablyslowly added during polymerization to avoid an excessive increase inviscosity of the latex which otherwise occurs when the entire amount ofthese comonomers is added to the initial charge to the polymerizationvessel. (The catalyst is also preferably continuously or intermittentlyadded during the polymerization.) From 40 to 100 percent of the amountof these comonomers can be added in this fashion, the balance, if any,being introduced with the initial charge.

The emulsifier used in the polymerization can also be added, in itsentirety, to the initial charge to the polymerization zone or a portionof the emulsifier (e.g., from to 25 percent thereof) can be addedcontinuously or intermittently during polymerization.

The surfactant is preferably continuously or intermittently added duringthe polymerization, although at least a portion thereof may be chargedto the reactor at the start of polymerization.

The latex produced by this polymerization can contain from about 35 to65 weight percent solids comprised chiefly of the interpolymers. Thepreferred contents of solids are from 40 to 60, and most preferably from50 to 60, weight percent.

APPLICATION OF BINDER TO FIBERS The binder described above is suitablyused to prepare nonwoven fabrics by a variety of methods known to theart which, in general, involve the impregnation of a loosely assembledmass of fibers with the binder latex followed by moderate heating to drythe mass. In the case of the present invention this moderate heatingalso serves to cure the binder by forming a cross-linked interpolymer.

The amount of binder, calculated on a dry basis, applied to the fibrousstarting web, suitably ranges from about 5 to about weight percent ofthe starting web, preferably from about 10 to about 70 weight percent.

If the surfactant has not been added already as part of the binderpolymerization process, it is incorporated physically into the binderlatex prior to application of the binder latex to the fiber mass. Thusan alcohol solution of the surfactant (with or without a plasticizer)may even be stirred into an available polymerized commercial binderlatex formulated from the aforementioned monomers, cross-linkingcomonomers, and possibly additional surfactants to increase thelongevity of the absorbency of the fabric to be produced.

The binder dispersion may be applied to the dry fibers after theformation or deposition of the web or mat so as to penetrate partiallyinto or completely through the interior of the fibrous products.Alternatively, the binder dispersion may be applied to the fibers asthey fall through the settling chamber to their point of deposition.This is advantageously obtained by spraying the binder dispersion intothe settling chamber at some intermediate point between the top and thebottom thereof. By so spraying the fibers as they descend to the pointof collection, it is possible to effect a thorough distribution of thebinder among the fibers before they are collected into the product. Inthe production of certain fibrous products wherein a hot molten mass ofa polymer, such as nylon or a fused siliceous mass or glass, isdisrupted by jets of heated air or steam, the binder dispersion may besprayed directly on the fibers while still hot and very shortly beforetheir deposition sothat quickly after deposition the binder sets and sobonds the fibers in proper relationship. Preferably, however,application of the binder dispersion to 1 1 the fibrous product is madeat room temperature to facilitate cleaning of the apparatus associatedwith the application of the binder dispersion. The binder dispersion maybe applied to one or both surfaces of the fibrous product, or it may bedistributed through the interior as well.

The binder of the present invention may be applied in conjunction withother binders, such as glue. Similarly, the use of potentially adhesivefibers within the fibrous product may also be resorted to in conjunctionwith the use of a binder of the present invention.

The aqueous dispersion of the binder may optionally contain from about/2 to 3% by weight of a wetting agent to assist penetration of thefibrous web or mat to which it is applied, and also it may optionallycontain either a foaming agent to provide the binder in a foamedcondition in the final product, or a defoamer when the ingredients ofthe aqueous dispersion have a tendency to give rise to foaming and in aparticular case such foaming is undesirable. The conventional wettingagents, including the alkali metal salts of di(C C alkyl sulfosuccinicacid, such as the sodium salt of dioctylsulfosuccinic acid, may be used.The wetting agent may also serve as the emulsifier in preparing thepolymer latex or it may be added after production of the latex.Conventional foaming and defoaming agents may be employed, such assodium soaps including sodium oleate for foaming and octyl alcohol orcertain silicones for defoaming.

Optionally the flexibility and softness of the fabric can be increasedby the addition of a hydrophobic external plasticizer to the bindercomposition without loss of desirable properties. Examples of externalplasticizers which are suitably used include dibutoxyethylphthalate,dibutyl phthalate, tricresyl phosphate and low molecular weightpolyesters. A typical plasticizer as isodecyl diphenyl phosphatemarketed by Monsanto Chemical Company under the trademark Santocizer148." These external components may be added just before application iftheir stability in the dispersion or solution is low, or they may beformulated into the aqueous dispersion of the binder and stored if theirstability in aqueous dispersion is high.

Various thermosetting resins may optionally be added to the binder latexto improve the strength of the resultant fabric. Typical of the usefulthermosetting resins are the condensates such as themelamine-formaldehyde and ureaformaldehyde condensates, the methylatedand methoxy alkyl cyclic ureas, and the methylolated and methoxyalkylcarbamates. Typically the thermosetting resins are used in quantitiesnot exceeding weight percent, based on the monomers used in thepolymerization, the resins being added in solution to the binder latexwith agitation before, during or after polymerization.

An acid catalyst may be optionally included in the aqueous dispersion atthe time it is applied to the fibrous web or it may be applied to thefibrous web before or after the copolymer is applied. Examples of acidiccatalysts that may be employed include oxalic acid, dichloroacetic acid,para-toluenesulfonic acid, and acidic salts such as ammonium sulfate orchloride and amine salts, such as the hydrochloride of 2-methyl-2-aminopropanol-1.

The impregnated web is then drried and cured. Thus, the fabrics aresuitably dried by passing them through an air oven or the like and thenthrough a curing oven. Ordinarily, drying is effected at 150200F. for4-6 min., followed by curing at 300310F. for 3-5 min. or more. However,other time-temperature relationships can be employed as is well known inthe art, shorter times at higher temperatures or longer times at lowertemperatures being used. For example, the curing step can be carried outat 280F. for about 15 min. or more. However, economic considerationsmake the use of excessively long times undesirable, and the uppertemperature limit is governed by the nature of the fibers. Temperatureswhich degrade the fibers are, of course, avoided. However, if the fibersare heat resistant, temperatures even as high as 350F. or higher can beused with times of 5-10 min. or more. In some cases, if desired. thedrying and curing can be effected in a single exposure or step, e.g., at300F. for 5-10 min.

A preferred binder composition (including the surfactant of the presentinvention) is set forth below, all parts being by weight:

60-80 parts butyl acrylate 40-20 parts vinyl acetate 1.0-3.0 partsacrylamide 1.0-4.0 parts N-methylol acrylamide 1.5-3.5 partsbis-tridecyl sodium sulfosuccinate EXAMPLES The following examplesillustrate the efflcacy of the present invention, and are intended to beillustrative only and not limitative of the invention. All parts are byweight unless otherwise indicated.

The procedures utilized in Examples 14-15 to determine fabric absorbencyare based on the following test format. A sample (4 in. X 4 in.) of thefabric is folded twice to give a 2 in. X 2 in. square which is thenpassed between steel rollers at 60 p.s.i. A paper clip is attached toweight the sample, which is then placed on the ,top of a water bath in a400 ml beaker at ambient temperature. The time required for the sampleto become saturated is the wet" time and the time required for thesample to sink completely below the surface of the water is the sinktime. The recorded wet and sink times are the average of four tests.

The initial absorbency test is conducted on asample which has beenconditioned to ambient or room temperature. The absorbency test aftertwo extractions is conducted on a sample which has undergone two of thefollowing extraction cycles. The sample (approximately 3 grams) issoaked while tumbling for 30 minutes in a half gallon jar containing1,500 ml ofidistilled water, after which the liquid is squeezed out andthe web is dried at room temperature. The absorbency test after steamsterilization is conducted on a sample which has been steam sterilizedfor 30 minutes at 130C prior to testing.

EXAMPLES l-l 2 The identity and quantity of each of the additionsutilized in each addition of these examples are indicated in Table 1.Addition A is added to a 2 liter flask equipped with agitator, condenserand nitrogen purge. 10% of Addition 8" is also added to the flask, andthe contents are then purged with nitrogen while heating to C. Thecontents are maintained for 15 minutes at C to insure initiation ofpolymerization, after which Additions C and D, and the remainder ofAddition B are added uniformly over a 4 hour period, the temperature ofthe contents being maintained at 75C.

13 I After the slow additions are completed, the contents are maintainedfor an additional 90 minutes at 75C, after which the contents are cooled(30C) and discharged.

EXAMPLE 13 The identity and quantity of the ingredients utilized in eachaddition of this example are indicated in Table ll. Addition A is addedto a 1 liter Paar reactor capable of withstanding 1,000 psig, andequipped with two pumps, a nitrogen purge, and evacuating means. Thecontents are then subjected to two purging cycles, each purging cycleconsisting of a nitrogen purge to 100 psig, followed by evacuation to 25inches of mercury. After completion of the two purging cycles, and whilethe contents are still under vacuum, mild agitation is commmenced andAddition B is permitted to be sucked into the reactor. The contents arethen heated to 70C while adding a sufficient quantity of ethylene(Addition C) to maintain a pressure of 750 psig. When the contents reach70C, of Addition E is added; after a 20 minute hold, Addition C is addeduniformly over 4 hours, and Addition is added uniformly over 6 hours,the pressure being maintained at 750 psig throughout the slow additionsby the addition of ethylene (Addition C"). After the slow additions arecompleted, the contents are held at 75C for 1 hour, and finally cooled,vented and discharged.

EXAMPLE 14 The identity and quantity of the ingredients utilized in eachaddition of this example are indicated in Table [1. Addition A is addedto the reactor of Example l3, and two purging cycles similar to those ofExample l3 are performed. Thereafter Addition B is allowed to be suckedinto the reactor. Next the contents are heated to 50C., with sufficientethylene (Addition C) being introduced to maintain a pressure of 500psig. Immediately upon the contents reaching the temperature of 50C.,Addition D is uniformly added over a period of 6.5 hours, and 30 minutesafter that temperature is reached, Additions E and F are added uniformlyover a period of 5.0 hours. Upon completion of the slow additions, thecontents are held for 15 minutes, and then Addition "6 is added over a50 minute period. The contents are then agitated at 50C for 30 minutes,and finally cooled to 45 C before venting and discharge.

EXAMPLE l5 Each of the binder latices prepared according to Examples l-l4 is diluted with water to 13 weight percent solids. Carded rayon testwebs weighing 200 grains per sq. yard are then saturated with thediluted binder latices to provide a weight percent dry resin add-on(i.e., 20 parts dry binder per 100 parts of web). The impregnated websare then dried at room temperature, and cured for 2 minutes at 130C in aforced hot air oven. The dried and cured test webs are then tested, theresults being indicated in Table II].

Table Ill illustrates that while all fabrics (except those formed withthe binders of Examples 8 and l2) displayed a good initial absorbency ofless than 300 seconds, only the fabrics containing the surfactant of thepresent invention also displayed a good absorbency of less than 300seconds after two extractions or steam sterilization. More particularly,Examples 8 and 9 illustrate that the use of normal and even excessiveamounts of a conventional anionic emulsifying agent such as SDBS (sodiumdodecyl benzene sulfonate) does not provide permanent absorbency.Examples l0-12 illustrate that the addition of a second conventionalanionic emulsifying or wetting agent such as Aerosol OT (di-octyl sodiumsulfosuccinate), di-decyl sodium sulfosuccinate, and di-dodecyl sodiumsulfosuccinate, respectively, does not provide permanent absorbency.

EXAMPLE 16 This example illustrates the utility of bistridecyl sodiumsulfosuccinate as an additive for commercially available latex bindersto improve the longevity of their absorbency characteristics.

Four commercial binder latices of the National Starch and ChemicalCorporation of Plainfield, N]. are tested according to the procedures ofExample 15 for their utility in forming permanent absorbing fabrics.Each of the samples tested had sink times in excess of 300 seconds aftertwo extractions. Next the same commercial binder latices are modified bythe addition of 1.53 weight percent of a surfactant (based on the resinsolids), the surfactant being added as a 20% active mixture ofsurfactant, benzyl butyl phthalate, and isopropanol (20/60/20 on aweight basis). When the solution contained di-octyl sodiumsulfosuccinate as surfactant, the samples produced had sink times inexcess of 300 seconds after two extractions. When the solution containedbistridecyl sodium sulfosuccinate as surfactant, the samples had the lowsink times indicated in Table IV.

This example also illustrates the efficacy of bisalkyl sodiumsulfosuccinates having higher molecular weight alkyl group substituentsrelative to those having lower molecular weight alkyl groupsubstituents. This example further illustrates that the surfactant ofthe present invention may be added to the binder latex afterpolymerization of the binder latex has been completed.

To summarize, a permanently absorbent nonwoven fabric has been describedwhich is particularly well suited for the industrial, hospital andconsumer usages where high absorbency after repeated usage is required.The permanent absorbency is achieved by utilization of a specificsurfactant which may be incorporated into the fabric either as acomponent of the crosslinkable binder during polymerization or as ablend of a crosslinkable polymeric binder and the special surfactant.

Now that the preferred embodiments of the present invention have beendescribed in detail, various modifications and improvements thereon willbecome readily apparent to those skilled in the art. Accordingly, thespirit and scope of the present invention is to be considered as definednot by the foregoing disclosure, but only by the appended claims.

TABLE I EXAMPLES 1 2 3 4 5 6 7 8 9 10 11 12 INGREDIENTS ADDITION A"wATER 430 430 430 430 430 430 430 430 430 430 430 430 SDBS 1.0 1.0 1.01.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 TRITON x-305 1.8 1.8 1.8 1.8 1.8 1.81.8 1.8 1.8 1.8 1.8 1.8 AMMONIUM PERSULFATE 0.4 0.4 0.4 0.4 0.4 0.4 0.40.4 0.4 0.4 0.4 0.4 w VINYL ACETATE 400 200 80 200 200 200 200 200 200200 BUTYL ACRYLATE 200 240 200 200 200 200 200 200 200 ETHYL ACRYLATE400 320 120 ACRYLONITRILE BIS-TRIDECYL soD1uM SULFOSUCCINATE 10.0 15.025.0 7.5 25.0 25.0 25.0 DI-DODECYL SODIUM SULFOSUCCINATE 6'0 DI-DECYLSODIUM SULFO SUCCINATE (50%) GLYCIDYL 10.0 METHACRYLATE ACRYL1C AC1DADDITION C" WATER 120 120 100 100 100 120 120 120 120 100 SDBS (20%)15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 60.0 15.0 15.0 15.0 TRITON X-3056.5 6 5 6.5 6.5 6 6.5 6.5 6.5 6.5 6.5 6 5 6 ACRYLAMIDE 15.0 N-METHYOLACRYLAM1DE (60%) 0 0 20.0 25 0 7.5 20.0 20.0 20.0 20.0 25.0 AEROSOL-OTADDITION D" wATER 50 50 50 50 50 50 5o 50 50 50 50 50 AMMONIUMPERSULFATE 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

TABLE II TABLE lI-continued EXAMPLE EXAMPLE INGREDIENTS WATER 45ADDITION A 3 SDBS (20%) 2.0 WMATER 330 260 3 SODIUM ACETATE 1.0 soDACETATE 6 5 SODIUM FORMALDEHYDE 0.41 IGEPAL C0-977 8.5 SULFOXYLATE SDBS(20%) 3.2 2 2 ADDITION E SODIUM BISULFATE 2.40 wATER 40 1.5 FERROUSSULFATE 44 pp AMMONIUM FERSULFATE 2.40 SODIUM PERSULFATE 40 VINYLCHLORIDE 30 ADD1T10N B ISO-BUTOXY METHYL ACRYLAMIDE 8.5 vlNYL ACETATE 20BIS-TRXDECYL SODIUM l0 VINYL CHLORIDE 30 SULFOSUCCINATE ADDITION CADDITION F ETHYLENE (Cp GRADE) 750 psig 500 psig WATER 35 ADDITION DSDBS (20%) 35 VINYL ACETATE 280 45 131s-TR1DECYL soD1uM 15.0BIS-TRIDECYL SODIUM 10 SULFOSUCCINATE SULFOSUCCINATE N-METHYLOLACRYLAMIDE (60%) 16.7 SANTOCIZOR 1 IGEPAL c0077 4.0 ISOPROPYL ALcoHoL 5TABLE III INITIAL ABSORBENCY ABSORBENCY AFTER 2 ABSORBENCY AFTER sTEAMEXTRACTIONS sTER1L1zAT10N EXAMPLE NO. wET s11-11 wET s11-11 WET SINK 1 120 6.6 12.9 2 1 1.9 5.9 107 3 1 2.5 26.2 40.8 2.0 10 4 2.1 25.5 70.5 5l.0 1.5 1 5.4 6 1 1.7 2.7 58.l 7 1 1.5 1.5 7.6 8 300 300 300 300 9 1.02.8 300 300 10 2.0 5.0 300 300 300 300 ll l.0 2.05 300 300 12 300 300300 300 l3 l 3.0 4.1 7.4 14 1 3.0 37.5 37.5

TABLE IV SlNK TlME BINDER LATlCES After 2 Extractions A crosslinkablebinder latex containing an acrylate copolymer, and at least oneconventional emulsifier. "A crosslinkable binder latex containing avinyl acetate/acrylate copolymer. and at least one conventionalemulsifier.

We claim:

1. An absorbent nonwoven fabric consisting essentially of a. a web offibers,

b. about 5.0 to about 100 weight percent, based on the fibers, ofcrosslinkable binder, and

c. about 0.2 to about 10.0 weight percent, based on said fibers andbinder, of at least one surfactant consisting of at least one salt of abis-alkyl sulfosuccinate having alkyl substituents each alkyl containingl3-l4 carbon atoms.

2. The fabric of claim 1 wherein said surfactant con sists of at leastone alkali metal salt of bis-tridecyl sulfosuccinate.

3. The fabric of claim 1 wherein at least one of said alkyl constituentsis branched.

4. The fabric of claim 1 wherein said surfactant consists ofbis-tridecyl sodium sulfosuccinate hving at least one branched alkylsubstituent.

5. The fabric of claim 3 wherein said binder consists essentially of acopolymer of at least two a,fl-monoethylenically unsaturated monomers,one of said monomers being effectively monofunctional and another ofsaid monomers being effectively polyfunctional, said effectivelymonofunctional monomers comprising from about 85 to about 99 weightpercent and said effectively polyfunctional monomers comprising fromabout 1 to about weight percent of said binder.

6. The fabric of claim 5 wherein said copolymer is a crosslinkableemulsion copolymer.

7. The fabric of claim 5 wherein at least one of saida,B-monoethylenically unsaturated monofunctional 18 monomers is selectedfrom the group consisting of alkyl acrylate, vinyl acetate, ethylene,vinyl chloride. and mixtures thereof, said alkyl acrylate having a C,C,alkyl group.

8. The fabric of claim 5 wherein at least one of saida,B-monoethylenically unsaturated polyfunctional monomers is selectedfrom the group consisting of acrylamide, isobutoxy methyl acrylamide,and N-methyol acrylamide.

9. The fabric of claim 3 containing about 0.3 to about 2.0 weightpercent, based on said fibers and binder, of said surfactant.

10. The fabric of claim 3 containing about 10 to about weight percent,based on said fibers, of said binder.

11. The fabric of claim 1 comprising on a weight basis:

a. a loosely assembled web of said fibers;

b. about 10 to about 70 weight percent, based on said fibers, of saidbinder containing at least one 01,3- monoethylenically unsaturatedmonofunctional monomer selected from the group consisting of alkylacrylate, vinyl acetate, ethylene, vinyl chloride, and mixtures thereof,said alkyl acrylate having a C,-C alkyl group, and at least oneafimonoethylenically unsaturated polyfunctional monomer selected fromthe group consisting of acrylamide, N-methylol acrylamide and isobutoxymethyl acrylamide, said monofunctional monomers comprising from about toabout 98 weight percent and said polyfunctional monomers comprisingabout 2 to about 5 weight percent of said binder; and

c. about 0.3 to about 2.0 weight percent, based on said fibers andbinder, of bis-tridecyl sodium sulfosuccinate having at least onebranched alkyl substituent.

12. The fabric of claim 3 wherein said binder and said surfactantcomprise on a weight basis about 60-80 parts butyl acrylate, 402O partsvinyl acetate, 1.0-3.0 parts acrylamide, 1.0-4.0 parts N-methylolacrylamide, and l.53.5 parts bis-tridecyl sodium sulfosuccinate.

1. AN ABSORBENT NONWOVEN FABRIC CONSISTING ESSENTIALLY OF A. A WEB OF FIBERS, B. ABOUT 5.0 TO ABOUT 100 WEIGHT PERCENT, BASED ON THE FIBERS, OF CROSSLINKABLE BINDER, AND C. ABOUT 0.2 TO ABOUT 10.0 WEIGHT PERCENT, BASED ON SAID FIBERS AND BINDER, OF AT LEAST ONE SURFACTANT CONSISTING OF AT LEAST ONE SALT OF A BIS-ALKYL SULFOSUCCINATE HAVING ALKYL SUBSTITUENTS EACH ALKYL CONTAINING 13-14 CARBON ATOMS.
 2. The fabric of claim 1 wherein said surfactant consists of at least one alkali metal salt of bis-tridecyl sulfosuccinate.
 3. The fabric of claim 1 wherein at least one of said alkyl constituents is branched.
 4. The fabric of claim 1 wherein said surfactant consists of bis-tridecyl sodium sulfosuccinate hving at least one branched alkyl substituent.
 5. The fabric of claim 3 wherein said binder consists essentially of a copolymer of at least two Alpha , Beta -monoethylenically unsaturated monomers, one of said monomers being effectively monofunctional and another of said monomers being effectively polyfunctional, said effectively monofunctional monomers comprising from about 85 to about 99 weight percent and said effectively polyfunctional monomers comprising from about 1 to about 15 weight percent of said binder.
 6. The fabric of claim 5 wherein said copolymer is a crosslinkable emulsion copolymer.
 7. The fabric of claim 5 wherein at least one of said Alpha , Beta -monoethylenically unsaturated monofunctional monomers is selected from the group consisting of alkyl acrylate, vinyl acetate, ethylene, vinyl chloride, and mixtures thereof, said alkyl acrylate having a C1-C12 alkyl group.
 8. The fabric of claim 5 wherein at least one of said Alpha , Beta -monoethylenically unsaturated polyfunctional monomers is selected from the group consisting of acrylamide, isobutoxy methyl acrylamide, and N-methyol acrylamide.
 9. The fabric of claim 3 containing about 0.3 to about 2.0 weight percent, based on said fibers and binder, of said surfactant.
 10. The fabric of claim 3 containing about 10 to about 70 weight percent, based on said fibers, of said binder.
 11. The fabric of claim 1 comprising on a weight basis: a. a loosely assembled web of said fibers; b. about 10 to about 70 weight percent, based on said fibers, of said binder containing at least one Alpha , Beta -monoethylenically unsaturated monofunctional monomer selected from the group consisting of alkyl acrylate, vinyl acetate, ethylene, vinyl chloride, and mixtures thereof, said alkyl acrylate having a C1-C12 alkyl group, and at least one Alpha , Beta -monoethylenically unsaturated polyfunctional monomer selected from the group consisting of acrylamide, N-methylol acrylamide and isobutoxy methyl acrylamide, said monofunctional monomers comprising from about 95 to About 98 weight percent and said polyfunctional monomers comprising about 2 to about 5 weight percent of said binder; and c. about 0.3 to about 2.0 weight percent, based on said fibers and binder, of bis-tridecyl sodium sulfosuccinate having at least one branched alkyl substituent.
 12. The fabric of claim 3 wherein said binder and said surfactant comprise on a weight basis about 60-80 parts butyl acrylate, 40-20 parts vinyl acetate, 1.0-3.0 parts acrylamide, 1.0-4.0 parts N-methylol acrylamide, and 1.5-3.5 parts bis-tridecyl sodium sulfosuccinate. 